Interpretive Summary: Barley yellow dwarf (BYD) is the most damaging virus disease of cereal crops. Oats are especially sensitive to BYD. The most effective means of limiting losses in oat production caused by BYD has been the planting of tolerant oat varieties. At least five Barley yellow dwarf viruses (BYDVs) from two virus groups cause BYD. BYDV-tolerant oat varieties usually are developed by screening breeding lines with one strain of BYDV. However, these varieties may have different interactions with other BYDV strains. The goal of this project was to study the accumulation and replication of BYDV-PAV, the most common BYDV strain in the Midwest, and BYDV-RPV, a less common BYDV strain, on oat lines that were developed to be tolerant and sensitive to BYDV-PAV. Our finding showed that oat plants tolerant to the BYDV-PAV strain accumulated virus components to levels indistinguishable from the sensitive oat lines. However, tolerant oat lines accumulated significantly lower levels of the components of BYDV-RPV than the corresponding sensitive lines. These experiments demonstrated that oat lines tested affected the replication of the two viruses differently. This information will be useful to other scientists who are involved in the development of new tolerant oat varieties or the study of the interaction of BYDVs and their hosts.

Technical Abstract:
To investigate the mechanisms of tolerance of oats to infection by barley yellow dwarf virus (BYDV), two pairs of sister oat lilies previously categorized as tolerant (T) and susceptible (S) to BYD-PAV [(63y2147-2 (TI) and 65y1103-I (S1); 65y2115-4 (T2) and 65y2137-2 (S2)] were infected with two BYDV strains (BYDV-PAV-IL and BYDV-RPV-NY). Virions and RNAs were quantified by triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) and by dot blot hybridization, respectively. Titers of BYDV-PAV-IL virions and RNA in shoots and roots of tolerant lines generally were equivalent to or higher than their titers in susceptible sister oat lines from 2 to 15 days after inoculation. Thus, there was no indication of inhibition of replication or movement of BYDV-PAV-IL in tolerant lines during the acute phase of BYD. Titers of BYD-RPV-NY and RNA in shoots of BYDV-PAV-tolerant lines also were equivalent to or higher than titers in the shoots of susceptible oat lines from 3 to 21 days after inoculation. However, titers of BYDV-RPV-NY and RNA in roots of BYDV-PAV-tolerant oat lines generally were equivalent to or lower than those in susceptible sister oat lines on sampling dates more than 2 weeks after inoculation. Our results indicate that replication and or movement of BYDV-RPV-NY but not of BYDV-PAV-IL is affected in the roots of oat lines previously termed tolerant to BYDV-PAV infection, therefore these lines possess some resistance to BYDV-RPV-NY. The mechanism of tolerance to BYDV-PAV was not apparent during the acute phase of the disease.